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// Copyright (c) 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// QuicStreamSequencerBuffer is a circular stream buffer with random write and
// in-sequence read. It consists of a vector of pointers pointing
// to memory blocks created as needed and an interval set recording received
// data.
// - Data are written in with offset indicating where it should be in the
// stream, and the buffer grown as needed (up to the maximum buffer capacity),
// without expensive copying (extra blocks are allocated).
// - Data can be read from the buffer if there is no gap before it,
// and the buffer shrinks as the data are consumed.
// - An upper limit on the number of blocks in the buffer provides an upper
// bound on memory use.
// This class is thread-unsafe.
// QuicStreamSequencerBuffer maintains a concept of the readable region, which
// contains all written data that has not been read.
// It promises stability of the underlying memory addresses in the readable
// region, so pointers into it can be maintained, and the offset of a pointer
// from the start of the read region can be calculated.
// Expected Use:
// QuicStreamSequencerBuffer buffer(2.5 * 8 * 1024);
// std::string source(1024, 'a');
// absl::string_view string_piece(, source.size());
// size_t written = 0;
// buffer.OnStreamData(800, string_piece, GetEpollClockNow(), &written);
// source = std::string{800, 'b'};
// absl::string_view string_piece1(, 800);
// // Try to write to [1, 801), but should fail due to overlapping,
// // res should be QUIC_INVALID_STREAM_DATA
// auto res = buffer.OnStreamData(1, string_piece1, &written));
// // write to [0, 800), res should be QUIC_NO_ERROR
// auto res = buffer.OnStreamData(0, string_piece1, GetEpollClockNow(),
// &written);
// // Read into a iovec array with total capacity of 120 bytes.
// char dest[120];
// iovec iovecs[3]{iovec{dest, 40}, iovec{dest + 40, 40},
// iovec{dest + 80, 40}};
// size_t read = buffer.Readv(iovecs, 3);
// // Get single readable region.
// iovec iov;
// buffer.GetReadableRegion(iov);
// // Get readable regions from [256, 1024) and consume some of it.
// iovec iovs[2];
// int iov_count = buffer.GetReadableRegions(iovs, 2);
// // Consume some bytes in iovs, returning number of bytes having been
// consumed.
// size_t consumed = consume_iovs(iovs, iov_count);
// buffer.MarkConsumed(consumed);
#include <cstddef>
#include <functional>
#include <list>
#include <memory>
#include <string>
#include "absl/strings/string_view.h"
#include "quic/core/quic_interval_set.h"
#include "quic/core/quic_packets.h"
#include "quic/core/quic_types.h"
#include "quic/platform/api/quic_export.h"
#include "quic/platform/api/quic_iovec.h"
namespace quic {
namespace test {
class QuicStreamSequencerBufferPeer;
} // namespace test
class QUIC_EXPORT_PRIVATE QuicStreamSequencerBuffer {
// Size of blocks used by this buffer.
// Choose 8K to make block large enough to hold multiple frames, each of
// which could be up to 1.5 KB.
static const size_t kBlockSizeBytes = 8 * 1024; // 8KB
// The basic storage block used by this buffer.
struct QUIC_EXPORT_PRIVATE BufferBlock {
char buffer[kBlockSizeBytes];
explicit QuicStreamSequencerBuffer(size_t max_capacity_bytes);
QuicStreamSequencerBuffer(const QuicStreamSequencerBuffer&) = delete;
QuicStreamSequencerBuffer(QuicStreamSequencerBuffer&&) = default;
QuicStreamSequencerBuffer& operator=(const QuicStreamSequencerBuffer&) =
QuicStreamSequencerBuffer& operator=(QuicStreamSequencerBuffer&&) = default;
// Free the space used to buffer data.
void Clear();
// Returns true if there is nothing to read in this buffer.
bool Empty() const;
// Called to buffer new data received for this stream. If the data was
// successfully buffered, returns QUIC_NO_ERROR and stores the number of
// bytes buffered in |bytes_buffered|. Returns an error otherwise.
QuicErrorCode OnStreamData(QuicStreamOffset offset,
absl::string_view data,
size_t* bytes_buffered,
std::string* error_details);
// Reads from this buffer into given iovec array, up to number of iov_len
// iovec objects and returns the number of bytes read.
QuicErrorCode Readv(const struct iovec* dest_iov,
size_t dest_count,
size_t* bytes_read,
std::string* error_details);
// Returns the readable region of valid data in iovec format. The readable
// region is the buffer region where there is valid data not yet read by
// client.
// Returns the number of iovec entries in |iov| which were populated.
// If the region is empty, one iovec entry with 0 length
// is returned, and the function returns 0. If there are more readable
// regions than |iov_size|, the function only processes the first
// |iov_size| of them.
int GetReadableRegions(struct iovec* iov, int iov_len) const;
// Fills in one iovec with data from the next readable region.
// Returns false if there is no readable region available.
bool GetReadableRegion(iovec* iov) const;
// Returns true and sets |*iov| to point to a region starting at |offset|.
// Returns false if no data can be read at |offset|, which can be because data
// has not been received yet or it is already consumed.
// Does not consume data.
bool PeekRegion(QuicStreamOffset offset, iovec* iov) const;
// Called after GetReadableRegions() to free up |bytes_consumed| space if
// these bytes are processed.
// Pre-requisite: bytes_consumed <= available bytes to read.
bool MarkConsumed(size_t bytes_consumed);
// Deletes and records as consumed any buffered data and clear the buffer.
// (To be called only after sequencer's StopReading has been called.)
size_t FlushBufferedFrames();
// Free the memory of buffered data.
void ReleaseWholeBuffer();
// Whether there are bytes can be read out.
bool HasBytesToRead() const;
// Count how many bytes have been consumed (read out of buffer).
QuicStreamOffset BytesConsumed() const;
// Count how many bytes are in buffer at this moment.
size_t BytesBuffered() const;
// Returns number of bytes available to be read out.
size_t ReadableBytes() const;
friend class test::QuicStreamSequencerBufferPeer;
// Copies |data| to blocks_, sets |bytes_copy|. Returns true if the copy is
// successful. Otherwise, sets |error_details| and returns false.
bool CopyStreamData(QuicStreamOffset offset,
absl::string_view data,
size_t* bytes_copy,
std::string* error_details);
// Dispose the given buffer block.
// After calling this method, blocks_[index] is set to nullptr
// in order to indicate that no memory set is allocated for that block.
// Returns true on success, false otherwise.
bool RetireBlock(size_t index);
// Should only be called after the indexed block is read till the end of the
// block or missing data has been reached.
// If the block at |block_index| contains no buffered data, the block
// should be retired.
// Returns true on success, or false otherwise.
bool RetireBlockIfEmpty(size_t block_index);
// Calculate the capacity of block at specified index.
// Return value should be either kBlockSizeBytes for non-trailing blocks and
// max_buffer_capacity % kBlockSizeBytes for trailing block.
size_t GetBlockCapacity(size_t index) const;
// Does not check if offset is within reasonable range.
size_t GetBlockIndex(QuicStreamOffset offset) const;
// Given an offset in the stream, return the offset from the beginning of the
// block which contains this data.
size_t GetInBlockOffset(QuicStreamOffset offset) const;
// Get offset relative to index 0 in logical 1st block to start next read.
size_t ReadOffset() const;
// Get the index of the logical 1st block to start next read.
size_t NextBlockToRead() const;
// Returns offset of first missing byte.
QuicStreamOffset FirstMissingByte() const;
// Returns offset of highest received byte + 1.
QuicStreamOffset NextExpectedByte() const;
// Return all received frames as a string.
std::string ReceivedFramesDebugString() const;
// Resize blocks_ if more blocks are needed to accomodate bytes before
// next_expected_byte.
void MaybeAddMoreBlocks(QuicStreamOffset next_expected_byte);
// The maximum total capacity of this buffer in byte, as constructed.
size_t max_buffer_capacity_bytes_;
// Number of blocks this buffer would have when it reaches full capacity,
// i.e., maximal number of blocks in blocks_.
size_t max_blocks_count_;
// Number of blocks this buffer currently has.
size_t current_blocks_count_;
// Number of bytes read out of buffer.
QuicStreamOffset total_bytes_read_;
// An ordered, variable-length list of blocks, with the length limited
// such that the number of blocks never exceeds max_blocks_count_.
// Each list entry can hold up to kBlockSizeBytes bytes.
std::unique_ptr<BufferBlock*[]> blocks_;
// Number of bytes in buffer.
size_t num_bytes_buffered_;
// Currently received data.
QuicIntervalSet<QuicStreamOffset> bytes_received_;
bool delay_allocation_until_new_data_ = GetQuicReloadableFlag(
} // namespace quic